POS0898 EARLY DETECTION OF ANTI-TNF INDUCED CHANGES IN NEW BONE FORMATION IN PSORIATIC ARTHRITIS PATIENTS BY<sup>18</sup>F-FLUORIDE PET-CT
Authors: J. De Jongh, G. C. J. Zwezerijnen, R. Hemke, M. Yaqub, M. G. H. Van de Sande, A. Van Kuijk, A. Voskuyl, C. J. Van der Laken
Journal: Annals of the Rheumatic Diseases (2023)

<h3>Background</h3> New bone formation in psoriatic arthritis (PsA) can be observed in all musculoskeletal disease domains and can lead to disability due to ankylosis and bridging syndesmophytes [1, 2]. The positive effect of anti-tumor necrosis (anti-TNF) therapy on radiographic damage (e.g. erosion and joint space narrowing) is well known, but there are contradictory findings on its effects on new bone formation [3, 4]. Imaging of new bone formation in PsA is pivotal in order to ascertain the extent and potential therapeutic effects on structural changes at an early stage of treatment. Our group recently demonstrated that molecular new bone formation can be observed in all PsA disease domains, using <sup>18</sup>F-Fluoride PET-CT scans. Moreover, the ability of this imaging technique to detect early therapeutic effects in ankylosing spondylitis patients was also demonstrated by our group [5]. <h3>Objectives</h3> To investigate whether <sup>18</sup>F-Fluoride PET-CT scans can detect a change in <sup>18</sup>F-Fluoride uptake, reflecting a change in new bone formation, after 12 weeks of anti-TNF therapy in clinically active PsA patients. <h3>Methods</h3> Nine patients (male 4/9, median age 47 (IQR 19)) with PsA fulfilling CASPAR criteria or a clinical diagnosis according to the treating rheumatologist and clinically active disease including ≥1 clinically active enthesitis site were included. In each patient, a whole body <sup>18</sup>F-Fluoride PET-CT scan was performed prior to and 12 weeks after starting anti-TNF therapy. Scans were independently assessed for PET-positive lesions (dichotomous) by two readers (blinded for clinical data). Fixed sized volumes of interest were drawn on top of visual PET positive lesions as well as on locations where visual PET positive lesions appeared or disappeared before or after treatment. Standardized uptake values corrected for individual integrated whole blood activity concentration (SUV<sub>AUC</sub>) were used for quantitative analysis. CT was used for anatomical reference. <h3>Results</h3> Combining all PET-positive lesions of all patients, a total of 153 lesions were observed at baseline (89, 30 and 34 in peripheral joints, entheses and spine, respectively). At week 12, a total of 119 PET-positive lesions were observed (69, 13 and 37 in peripheral joints, entheses and the spine, respectively). Grouping all lesions of all patients, there was a decrease in the mean SUV<sub>AUC</sub> between baseline (1.578, SD 0.99) and week 12 of anti-TNF treatment (1.230, SD 0.85) (Figure 1A). Similar results were observed when grouping all lesions of all patients for separate disease domains. Mean SUV<sub>AUC</sub> changes between baseline and 12 weeks were -0.294 (SD 0.88), -0.357 (SD 0.69) and -0.300 (SD 0.67) for respectively peripheral joints (Figure 1B), entheses (Figure 1C) and the spine (Figure 1D). <h3>Conclusion</h3> <sup>18</sup>F-Fluoride PET-CT detected a change in new bone formation in PsA domains during anti-TNF therapy as early as 12 weeks post-treatment. The data point at a mean decrease of new bone formation in peripheral joints, entheses and axial skeleton. <h3>References</h3> [1]de Jongh J et al. (18)F-sodium fluoride PET-CT visualizes both axial and peripheral new bone formation in psoriatic arthritis patients. Eur J Nucl Med Mol Imaging. 2022. [2]Lories RJ et al. Modulation of bone morphogenetic protein signaling inhibits the onset and progression of ankylosing enthesitis. J Clin Invest. 2005;115(6):1571-9. [3]Goulabchand R et al. Effect of tumour necrosis factor blockers on radiographic progression of psoriatic arthritis: a systematic review and meta-analysis of randomised controlled trials. Ann Rheum Dis. 2014;73(2):414-9. [4]Sieper J et al. Critical appraisal of assessment of structural damage in ankylosing spondylitis: implications for treatment outcomes. Arthritis Rheum. 2008;58(3):649-56. [5]Bruijnen STG et al. Bone formation in ankylosing spondylitis during anti-tumour necrosis factor therapy imaged by 18F-fluoride positron emission tomography. Rheumatology (Oxford). 2018;57(4):631-8. <h3>Acknowledgements:</h3> NIL. <h3>Disclosure of Interests</h3> Jerney de Jongh: None declared, Gerben C.J. Zwezerijnen: None declared, Robert Hemke: None declared, Maqsood Yaqub: None declared, Marleen G.H. van de Sande Speakers bureau: UCB, Novartis, Janssen, Consultant of: UCB, Novartis, Abbvie, Eli Lily, Grant/research support from: UCB, Novartis, Eli Lily, Arno Van Kuijk Consultant of: UCB, Janssen, Grant/research support from: Janssen, Novartis, Pfizer, Alexandre Voskuyl Consultant of: GSK, Astra Zeneca, Grant/research support from: Boehringer Ingelheim, Conny J. van der Laken Speakers bureau: Janssen, Abbvie, Pfizer, Novartis, UCB Pharma, Galapagos, Paid instructor for: Lilly, Galapagos, Consultant of: UCB Pharma, GSK, Novartis, Grant/research support from: Pfizer, Abbvie, Novartis, GSK, UCB Pharma